Full width array write heads using various technologies, such as for example, light emitting diodes (LEDs), inkjet, etc. are being widely used in printers. Such full width array write heads provide an economical way to quickly print across an entire width of a page with a high degree of resolution.
Typically the full width writing array is assembled on a mounting bar to provide structural rigidity, mounting capacity and some temperature stability. In the case of the full width writing array relying on LED technology, the same array can be used for cyan, magenta, yellow or black. Unfortunately, each array is subject to different temperature conditions. The array closest to the fuser often requires special treatment using fans or other cooling methods.
FIG. 1A shows a conventional full width array write head assembly 100. In particular, the conventional full width array write head 100 includes a mounting bar 110, a full width array write head 140, and mounting holes 130.
Full width array write head 140 consists of imaging chips 120. The imaging chips 120 can be butted end-to-end and bonded to the mounting bar 110. Alternatively, imaging chips 120 can be disposed in two or more rows, for example, in a staggered configuration. The imaging chip can also be a single chip, for example, an organic light emitting diode (OLED). Each of the imaging chips 120 include a plurality of LEDs, shown in more detail in FIG. 1B. The mounting holes 130 on the ends of the mounting bar 110 are used to mount the full width array write head 100 to a printer (not shown).
The imaging chips 120 are individually activated by printhead circuitry (not shown) to form an image. The image is then transferred to an imaging medium, e.g., paper. Such transfer of an image from an imaging chip 120 to an imaging medium is well known within the art.
FIG. 1B shows a portion of a conventional imaging chip 120.
Printers are typically rated at dots per inch (dpi) resolution. A typical dpi for a printer can be 600 dpi. For example, a LED imaging chip 120 used in a printer that is rated at 600 dpi contains a density of LEDs such that an imaging medium passing one inch across the imaging chip can produce 600 individual dots per inch.
Because of the difficulty in illustrating the face of a conventional imaging chip 120 that has such a large number of LEDs that produce a high resolution, e.g., 600 dpi, FIG. 1B shows an example of a portion of an imaging chip 120 that has 15 LEDs on its face.
As the full width array write head assembly 100 heats up, its length increases due to thermal expansion. A particular source of heat is a fuser, with the area nearest the fuser being heated the most. For example, a 600 dpi system over an 11 inch width might become a 595 dpi system over 11.092437 inches after being heated. Such a loss in resolution and change in magnification is undesirable,
Attempts have been made to compensate for thermal stresses and expansion on a full width array write head. One such patent, U.S. Pat. No. 5,528,272 discloses use of a full width array write head that is constructed of materials having a high thermal coefficient of expansion and a low thermal coefficient of expansion. An adhesive for holding various components together provides lateral give while firmly holding the respective components together. The use of an adhesive that provides for lateral give relieves shear stress caused by the expansion and contraction of materials having different coefficients of expansion.
Other attempts to deal with heat issues related to a full width array write head included use of a liquid to cool a metal substrate. Moreover, a dedicated fan has been employed to cool a full width array closest to a fuser. However, whatever attempts have been made to compensate for thermal stresses and expansion on a full width array write head, thermal stresses still exist on a full width array write head that result in changes in resolution and magnification.
Accordingly, the present teachings solve these and other problems of the prior art's compensation for thermal stresses on a full width array write head.